Marketable Securities - Summary of Marketable Securities Held (Detail) - USD ($) $ in Thousands	Oct. 31, 2020	Apr. 30, 2020
Marketable Securities [Line Items]
Amortized Cost	$ 39,517	$ 51,456
Unrealized Gains	220	470
Unrealized Losses	(37)	(1)
Estimated Fair Value	39,700	51,925
Corporate Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	30,726	38,922
Unrealized Gains	148	295
Unrealized Losses	(37)	(1)
Estimated Fair Value	30,837	39,216
Obligations of U.S. Government and Its Agencies [Member]
Marketable Securities [Line Items]
Amortized Cost	8,791	12,534
Unrealized Gains	72	175
Estimated Fair Value	$ 8,863	$ 12,709

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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